Many industries generate oil-based slurries. An oil-based slurry (OBS) composition may be a homogenized, viscous and stable semi-solid composition containing oil, water (usually emulsified) and fine solids. The solids fraction may be inert inorganic material such as clays, salts and minerals. Especially problematic are OBS compositions in which the largest solid particles are less than 10 micrometers in diameter, rendering most mechanical equipment such as centrifuges and presses impractical. Many OBS compositions are considered waste byproducts today, where further extraction of hydrocarbons is no longer practical. Hydrocarbon content in waste OBS compositions can range from about 5 percent to about 90 percent (weight basis is used herein unless otherwise noted) of the OBS composition, therefore making many OBS compositions ideal for further processing to extract valuable hydrocarbons for recovery and recycling. Traditional methods such as thermal desorption, incineration, chemical treatment, deep well injection, solidification and landfill disposal may either be very costly, require significant energy, use hazardous chemicals, have poor recovery efficiencies, generate low quality hydrocarbons, alter the original hydrocarbons, use chemicals that may negatively impact the environment or provide no recovery of valuable hydrocarbons in the waste OBS composition.
Where mechanical separation can be applied to OBS compositions, typically two or three separated components are generated where at least one component is a non-liquid containing solid with some quantity of the residual liquids. This semi-solid has the physical characteristics of sludge. Sludge is a heavy, viscous semi-solid material that contains similar components of slurry but with higher solids content. Sludge is generated from numerous sources, such as: oil refining; mud brought up by a mining drill; precipitate in a sewage tank; sediment in a steam boiler or crankcase, and other sources.
Current technologies for treating or disposing of slurries and/or sludges include the following. As used herein the term “oil” includes, but is not limited to, hydrocarbon oils.
Water and Solids Slurries and Sludges. For most slurries and sludges containing only water and solids, the objective is to maximize volume reduction which may be accomplished using traditional equipment such as simple settling basins, clarifiers, filter presses, belt presses, centrifuges, and the like. However, where the solids are fine (less than about 10 micrometers in diameter, and especially less than 1 micrometer), coagulants and/or flocculants may be required with these technologies to effectively increase the size of the solids so that settling using gravitation force or centrifugal force can generate a byproduct with as little water as possible. In addition, all of these technologies generate a byproduct (cake) with some water ranging from about 40 percent to about 80 percent, therefore if the objective is to remove 100 percent of the water, then the water must be evaporated using a thermal process typically known as sludge drying. Alternatively, if the cake can pass landfill acceptance criteria (typically a paint filter test or slump test and leachate criteria) the cake may be suitable for disposal in a landfill. When the feed slurry or sludge contains fine solids that cannot be agglomerated using coagulants and flocculants, then the feed must be dried directly using a thermal process without traditional equipment, and without the benefit of pre-treatment. In this case, significant water will remain in feed material and removal of the water through evaporation will require a significant amount of energy using sludge dryers. In many cases, a high water content slurry or sludge does not pass the landfill acceptance criteria.
Oil, Water and Solids Slurries and Sludges. When the slurry or sludge contains oil, water and solids, processing may be more complex. Processing objectives may be several, such as recovery of oil, recovery of solids (such as catalyst fines or metals), maximum volume reduction, or some combination of these. Complexity may be further increased with the liquid component where the oil and water are stable emulsions. Furthermore, the solid particles may be fine and/or low density, and may contribute to forming a “complex emulsion” of these solids, oil, and water. The use of traditional coagulants and flocculants may not work well in OBS compositions. Demulsifier chemicals (“demulsifiers”) may be required to separate the oil and water components; however, demulsifiers may not work in all cases, particularly when the slurry is a homogenized highly stable emulsion. For OBS compositions that are “loosely” emulsified, a combination of surfactants, coagulants and flocculants along with centrifugal forces may result in a good recovery of oil and volume reduction, however a waste sludge or cake with relatively high amount of solids is generated which requires further disposal or processing. Disposal options may be limited, as many landfills will not accept oily sludges. Disposal in salt caverns or bioremediation technologies are possible, along with incineration, but no valuable recoverable product is recovered from the waste sludge in all four options. Some options may result in increased greenhouse gas emissions and other airborne pollutants.
Processing options of the waste sludge from OBS compositions may be most effective when the valuable components, typically oil, but in some cases oil and/or solids, can be recovered. This may accomplished using evaporative technologies referred to as thermal desorption followed by condensation. When the feed slurry or sludge contains fine solids that cannot be separated using mechanical forces or combined chemical and mechanical forces, the feed slurry or sludge sees no volume reduction. Disposal options, such as salt caverns and incineration may be utilized but suffer similar drawbacks as previously mentioned. Although OBS compositions may be processed using known thermal desorption technology, in known methods the composition must be fed directly to the equipment. In this case, significant oil and water remain in the feed OBS composition, and the removal of the oil and water through evaporation requires significant amounts of energy in addition to the careful management of hydrocarbon vapors at elevated temperatures.
Recovery of hydrocarbons from non-inert and inert solids has been proposed in several patent documents for application in the plastics art, oil refining art, shale retorting art, and the like, however, they are typically selected from filtration, drying, extraction, centrifugation, calcining and other separation methods, and therefore either do not work well and/or require inordinate amounts of energy for the amount of oil or solids obtained.
At least for these reasons, it would be an advance in the art of recovery of hydrocarbons and/or valuable solids (such as catalyst fines or metals) from waste streams if the hydrocarbons and water could be removed or separated from hydrocarbon/water/inert solids mixtures efficiently to recover substantially all of the hydrocarbons, as well as produce a solids composition more suitable for reuse, recycling, or land filling.